Many known chemical products such as surfactants, plasticizers, solvents, and polymers are currently manufactured from non-renewable, expensive, petroleum-derived or natural gas-derived feedstock compounds. High raw material costs and uncertainty of future supplies requires the discovery and development of surfactants, plasticizers, solvents, and polymers that can be made from inexpensive renewable biomass-derived feedstocks and by simple chemical methods. Using renewable resources as feedstocks for chemical processes will reduce the demand on non-renewable fossil fuels currently used in the chemical industry and reduce the overall production of carbon dioxide, the most notable greenhouse gas.
It is desirable to provide commonly used materials, such as surfactants, plasticizers, solvents, and polymers, from renewable feedstocks as a source of chemical building blocks. It is desirable to provide chemical building blocks that are chemically and thermally stable. It is desirable to provide chemical building blocks having multiple functionalities for subsequent reactions. It is desirable to provide such materials by simple and reproducible methods that can be carried out with ease.
A potential source of materials that are useful as chemical building blocks are cyclic ketals and acetals of oxocarboxylates with polyols. It is known, for example, that polyhydric alcohols, or polyols, having 1,2 and 1,3 hydroxy conformations can react with a ketone or aldehyde to form a cyclic ketal or an acetal (Carey, F. A. and Sundberg, R. J., “Advanced Organic Chemistry Part B: Reactions and Synthesis” 2nd ed., 1983, Plenum Press, NY, N.Y., p. 544). The 1,2 and 1,3 configurations of hydroxyl groups on a hydrocarbon chain are shown below as (a) and (b), respectively.
Diols such as 1,2-ethane diol (ethylene glycol) and 1,3 propanediol (propylene glycol) are examples of such polyols. Diols having a 1,2 hydroxyl group configuration form dioxolanes when reacted with ketone or aldehyde moieties, while 1,3 diols form dioxanes.
Various ketals arising from the reaction of oxocarboxylic acids and esters thereof with diols and triols are known. Ono et al., J. Am. Oil Chem. Soc. 70(1), 29 (1993) disclose ketalization of ethyl pyruvate, ethyl acetoacetate, and ethyl levulinate with various 1-O-alkyl glycerols (diols). Okohara et al., JP 04217972, similarly disclose ketalization of ethyl levulinate with 1-O-alkyl glycerols, followed by saponification of the ester moiety. McCullough et al., U.S. Pat. No. 5,998,092 disclose the ketalization of two keto acids with ethylene glycol. Chirila, Revistade Chimie 28(8), 730-3 (1977) discloses the 1:1 adduct of acetoacetate esters with glycerol. Gelas, Carbohydrate Research 30(1), 21-34 (1973) and Rakhmankulov et al., SU 722912 disclose the 1:1 adduct of pyruvate esters with glycerol and subsequent bicyclic lactone formation.
Ketals of glycerol and levulinic acid or an ester thereof are described in U.S. Patent Publication No. 2008/0242721, the entirety of which is incorporated herein by reference. The ketal reaction product of glycerol with a levulinate results in the ketal acid or ketal carboxylate shown below, along with one mole of water per mole of ketal formed:
wherein R is hydrogen or an alkyl group. The use of levulinate compounds and glycerol based compounds is particularly useful as both of these starting materials arise from renewable feedstocks. Further, the ketal reaction products are useful for synthesis of a wide variety of surfactants, plasticizers, polymers, and the like. Other reaction products of oxocarboxylates (such as pyruvic acid, acetoacetic acid, or esters thereof, and the like) with triols (such as trimethylolpropane, trimethylolethane, and the like) are disclosed in International Patent Application No. PCT/U.S.08/75225. The methods employed to synthesize these compounds involve the formation of one mole of water with each mole of ketal formed. Likewise, polyketal compounds are formed from oxocarboxylates and tetrols and higher polyols using similar methods, with one mole of water formed for each mole of ketal functionality formed. Polyketal compounds are described in International Patent Application No. PCT/U.S.08/079,337. One example of a polyketal is a bisketal formed from a levulinate ester and erythritol (or a stereoisomer thereof):
Other compounds formed from such reactions include the reaction product of three moles of a pyruvate ester (r=alkyl) with sorbitol or mannitol, to result in three moles of water and a trisketal:
and the reaction of multiple moles of an acetoacetate ester (R=alkyl) with poly(vinyl alcohol) or an ethylene or propylene copolymer thereof, for example:
wherein m, n, and o are integers and o may be zero.
Synthetic routes to form ketals of oxocarboxylic acids or the esters thereof are described in International Patent Application No. PCT/U.S.08/079,083. The methodology disclosed therein employs very low levels of acid catalyst and certain stoichiometric ratios of oxocarboxylate to polyol to result in high yields of ketal compounds with short reaction times. However, this methodology, as well as previous methods used to form ketals from oxocarboxylates and polyols, necessarily involves the formation of water in conjunction with formation of the ketal end product. Because ketal formation is reversible in the presence of water and the acid catalyst, rigorous removal of water is necessary in order to drive the reaction and maintain high yields and product stability. Additionally, the main side products in the reaction of tetrols and higher polyols to form polyketals are typically those where less than the full desired complement of oxocarboxylate is reacted—e.g., a tetrol such as erythritol or diglycerol having one ketal functionality instead of two; or a hexitol such as mannitol having one or two ketal functionalities instead of three. Such side products are difficult to separate from the desired end product, necessitating fractionation. Further, the free hydroxyl groups present in these side products can undergo side reactions in subsequent polymerization reactions or create incompatibility with one or more formulation components in the application of bisketal and trisketal compounds as plasticizers, solvents, and the like.
Additionally, the structural variation of the ketal and polyketal compounds disclosed in the above cited patent applications and publications are limited to the variation in the polyol and oxocarboxylate compounds employed.
It is desirable to provide new starting materials and synthetic routes to form new varieties of chemical building blocks for monomers, plasticizers, surfactants, and polymers. It is desirable to provide chemical building blocks that arise solely from renewable feedstocks. It is desirable to facilitate synthesis of chemical building blocks that is simple, inexpensive, and scalable for commercialization purposes. It is desirable to avoid the problem of water formation in the ketalization of oxocarboxylic acids or their esters.